The present invention is generally directed to the field of communication networks and more particularly, is directed to wavelength allocation in a regional access network with optical add-drop multiplexers.
FIG. 1 illustrates a two-tier wide area network (WAN) as with a regional access network (RAN). As shown in FIG. 1, nodes are divided into backbone and regional nodes. Backbone nodes are equipped with optical cross connects (OXCs), and regional nodes are equipped with less expensive optical add-drop multiplexers (OADMs). The RAN is a bus network between two backbone nodes as encircled in FIG. 1.
Wavelengths are divided into backbone and local wavelengths. Backbone wavelengths pass through the regional nodes without being add/dropped. Regional nodes communicate through local wavelengths. If a connection is requested from an outside network for a node in the RAN, it is carried on a backbone wavelength to the backbone node and then on a local wavelength from the backbone to the regional node. Also, if a connection is requested by a regional node to the outside network, it is carried on a local wavelength from the regional to a backbone node and then on a backbone wavelength to the destination node, the connection being converted at the backbone node. Traffic is carried on bidirectional pairs of fibers.
Adding and dropping all wavelengths at each regional node is appropriate if it exchanges the information only with the adjacent node. A connection may traverse multiple nodes without being dropped at intermediate nodes. Thus, the required number of ports per node should be less than the total number of wavelengths to save cost. It is known in the prior art to minimize the number of OADM ports in RANs assuming static traffic. It is assumed, a priori, node-to-node demand for bandwidth and wavelengths are assigned to be add/dropped at nodes to meet the demand while minimizing the number of OADM ports. Saving of OADM ports in a RAN can be calculated for uniform and distance dependent static traffic patterns. If nodes may request a traction of the bit-rate transported by a single wavelength, the saving is calculated through ‘super-node’ modeling. Nodes are grouped into ‘super-nodes’ which request only full wavelength bit-rates.
The prior art as proposed two heuristics to minimize the number of OADM ports in a ring network. and to improve the heuristics by combining them with routing decisions. While WDM optical network in the prior art serve the SONET layer, it serves the ATM layer. At each node, packets on dropped wavelength are either received by that node or routed to the added wavelengths together with the packets generated by that node. Virtual connections are requested and released according to the specified statistics. Blocking probability of connection requests is calculated for the proposed system with reduced number of OADM ports.
With exponentially increasing demand for bandwidth, dynamically reconfigurable optical networks will soon become a reality. In such networks, wavelengths are assigned and released on demand. We analyze the performance of a RAN based on different OADM technologies and with dynamic traffic. Routing is done on-line, so that connections are not rearranged when a new connection is requested. Connections can carry a full bit-rate of wavelengths, or only the portion of it. A connection is carried on a single wavelength, and it is not converted at intermediate nodes. Such a choice simplifies network management. Given this assumption, each pair of nodes in a RAN with fixed-tuned OADMs should have at least one wavelength in common.